1. Field of the Invention
The present invention relates to two-component systems based on amines and epoxides, a method of preparing such two-component systems, and a method of coating articles with such two-component systems.
2. Discussion of the Background
Known two-component amine/epoxide systems emulsified in water, i.e. which form oil-in-water emulsions, after mixing of amine emulsions and epoxide emulsions, physically dry in a reasonable time at ambient temperature and chemically cure. Cold-cured coatings are evaluated based on the characteristics of films attainable by hot curing.
Currently attainable coatings produced by cold-curing of commercially available aqueous amine/epoxide emulsions are satisfactory, and some are even good. The advantage they offer in substituting water for organic solvents are evident.
However, a disadvantage of such systems is their high water content, which is commonly 50 wt. %, but ranges from 35 wt. % to more than 70 wt. %. This large amount of water generally must be evaporated without heating. This evaporation can be time-consuming, particularly in the event of low ambient temperature and poor ventilation. Frequently, residual water may remain in the cured film or on the substrate, which causes problems.
Another disadvantage of the known systems is that, when pigmented formulations are employed, loss of gloss and irregularities in the gloss of the surface occur, because of the wide range of water content. In addition, the elasticity and solvent resistance of the cold-cured films or coatings are reduced as the water content of the initial emulsion is increased. Furthermore, it is known that it is not possible to achieve thick film coatings with a high water content or a high solvent content.
The epoxide compounds which are suitable for use in these emulsions are relatively insoluble in water and can be easily emulsified in water, e.g., with the aid of nonionic emulsifiers. Polyamines are in general water soluble; thus they readily form aqueous solutions. However, they do not form emulsions in water; in fact, for example, they break up epoxide emulsions and cause phase separation.
In order to form emulsions of amines, the amines must be hydrophobized, i.e., they must be chemically transformed to relatively insoluble products.
Such insoluble products may be produced from amines by addition, condensation, or substitution reactions. The resulting reaction products of the polyamines are relatively water-insoluble, and are emulsifiable, but are of a consistency which makes it necessary to employ a low content of resin, i.e., a high water content, which, as discussed above, results in detrimental effects. In particular, a high water content makes it impossible to achieve a high coating density with a flowable coating.
Thus, there remains a need for aqueous emulsions based on amines and epoxides, which have a low water content and which are cold curable, can be applied in thick layers with a high filler content, and yield elastic coatings with good solvent resistance.